In many wireless communications systems the power amplifiers in the transmitter are required to be very linear, in addition to being able to simultaneously amplify many radio channels (frequencies) spread across a fairly wide bandwidth. They also have to do this efficiently, in order to reduce power consumption and need for cooling, and to increase the lifetime of the amplifiers. The linearity is required to be good since nonlinear amplifiers would cause leakage of interfering signal energy between channels.
The amplitude probability density of a mix of sufficiently many independent radio frequency (RF) channels, or of a multi-user CDMA signal (CDMA=Code Division Multiple Access), tends to be close to a Rayleigh distribution having a large peak-to-average power ratio. Since a conventional RF power amplifier (especially class B) generally has an efficiency proportional to its output amplitude, its average efficiency is very low for such signals.
In response to the low efficiency of conventional linear power amplifiers, several methods have been proposed. One of these is the Chireix outphasing method, sometimes and in some embodiments called “linear amplification using nonlinear components” (LINC). The Chireix method has been used extensively for AM broadcast transmitters. However, the method has so far been unsuccessful in delivering the theoretical high efficiency for high peak-to-average power ratios, especially while maintaining high linearity and when using practical RF transistors.